NY-14-C053 -- Typical Hot Water Draw Patterns Based on Field Data PDF

Daily hot water use is highly variable both between residences and within the same residence on different days. Determining typical hot water draw patterns to use in test procedures to rate water heaters has been difficult. Methods to compare draw patterns were developed based on data obtained from 12 separate field studies. The data set from 22,902 days in 159 houses was analyzed to determine typical inlet and outlet water temperatures. The data was then divided into three clusters reflecting house configurations that demonstrated small, medium, or large median daily hot water use. The daily hot water use within each cluster was then analyzed in terms of volume and number of hot water draws. The daily draw patterns in each cluster were also characterized using cumulative distributions for volume of draws, duration of draws, times since previous draw, and flow rates. The results of the analysis of the field data were compared to the conditions and draw patterns in the current ASHRAE method of test for rating residential water heaters. The results show a higher number of smaller draws at lower flow rates than used in the current test procedure. The results of the analysis are being considered by ASHRAE standard project committee 118.2, Method of Testing for Rating Residential Water Heaters, to revise the test procedure for residential water heaters to incorporate a range of draw patterns.